The invention relates to an arrangement and a method for driving a lubrication pump in a dual clutch transmission.
Commercial vehicles can be provided with a dual-clutch transmission (DCT) having two individually controllable master clutches, each associated with a set of gears. Usually, one clutch is used for odd gears (gears 1, 3, 5, etc.), while the other clutch is used for even gears (gears 2, 4, 5, etc.). For lubrication and cooling of a DCT an oil pump is needed, which pump is usually mechanically driven. In operation, one clutch is engaged, or active, and transfers power, while the other clutch is disengaged, or inactive. A gear associated with the inactive clutch can be engaged, allowing a gear to be preselected prior to being active. A gear shift is performed by simultaneously disengaging the active clutch and engaging the inactive clutch. This enables power-shifting between gears, that is, there is no interruption of power being transferred to the driven wheels.
Some DCT designs feature a direct gear, where the input shaft is clutched to the output shaft and the power is not transferred via any gear meshes. This will reduce the power losses to a large extent. Since gear meshes and bearings are not loaded in the direct gear, the need for lubricating and cooling oil flow will be reduced. In this mode of operation, the oil pump is driven by the direct gear via the engaged clutch at a speed proportional to the prime mover (e.g. engine) speed. A problem with this solution is that the pump is operated at a higher speed than necessary, which is a waste of energy.
An alternative solution is to use an electrically driven lubrication pump, as shown in US2012/322603. This makes the pump independent of the prime mover speed and clutch actuation, but requires an additional electric motor. The use of a separate motor for this purpose adds weight and cost and introduces durability and reliability issues.
It is desirable to provide an improved arrangement for driving a lubrication pump in a dual clutch transmission that solves or minimizes the above problems.
In the subsequent text, the term “clutch unit” is intended to describe a clutch arrangement comprising a rotatable friction plate, friction elements, actuators and other peripherals required for a vehicle clutch assembly. Furthermore, in the subsequent text, the terms “lubricated”, “lubricating” and “lubrication” shall be read in the context of lubrication per se, i.e., for reducing friction and wear, as well as for cooling, i.e., removing heat from components.
According to a preferred embodiment, an aspect of the invention relates to a vehicle transmission in a vehicle which comprises at least one prime mover, e.g., an internal combustion engine and/or an electric motor. The prime mover can be arranged to propel a vehicle with suitable ground engaging members, such as wheels or tracks. The examples given below refer to driving wheels only.
The transmission comprises a first transmission mechanism arranged to transmit mechanical driving power from an output shaft of the prime mover to a first input shaft and to put any one of a first set of gears in an engaged state to drivingly connect the first input shaft to the driving wheels. The transmission further comprises a second transmission mechanism arranged to transmit mechanical driving power from the output shaft of the prime mover to a second input shaft and to put any one of a second set of gears in an engaged state to drivingly connect the second input shaft to the driving wheels. A controllable first clutch unit is arranged to bring the output shaft of the prime mover and the first input shaft into engagement with each other. Similarly, a controllable second clutch unit is arranged to bring the output shaft of the prime mover and the second input shaft into engagement with each other. A lubrication pump for lubricating the transmission is drivingly connected to the first input shaft. In the subsequent text this lubrication pump can also be referred to as a “pump”.
An electronic control unit is arranged to control the operation of the transmission. The electronic control unit is further arranged to register the operational state of the lubrication pump, i.e. if the pump is currently driven or not, and to determine a lubricated state of the transmission. i.e. if lubrication is required or not. When the first clutch unit is engaged to drivingly connect the output shaft of the prime mover to the first input shaft and the driving wheels, the lubrication pump is driven by the first input shaft. In this case lubrication of the transmission is being carried out as normal and the pump speed is proportional to the rotational speed of the first input shaft and the output shaft of the prime mover.
However, when the second clutch unit is engaged to drivingly connect the output shaft of the prime mover to the second input shaft and the driving wheels, then the first input shaft and the associated lubrication pump are not driven by the output shaft of the prune mover. The electronic control unit is arranged to register the operational state of the first and second clutches and the lubrication pump. When it is registered that the second clutch unit is engaged, the electronic control unit can be arranged to at least partly engaging the first clutch unit, in order to drive the first input shaft and the lubrication pump.
The electronic control unit is also arranged to determine the lubricated state of the transmission. If the electronic control unit determines that the lubricated state of the transmission or a part thereof is insufficient, then the lubrication pump is driven by the first input shaft by at least partly engaging the first clutch unit. The electronic control unit can be connected to at least one of a number of existing sensors (not shown) for detecting and monitoring the lubrication of each clutch unit and the shafts and gears of the transmission. Examples of sensors are temperature sensors for measuring oil temperature and/or bearing temperature, oil level sensors for monitoring oil levels, oil pressure sensors for monitoring oil pressure, as well as other suitable sensors allowing the electronic control unit to determine the lubricated state of the transmission. These sensors can be arranged to monitor the said parameters in one or more locations and to transmit signals to the electronic control unit.
According to a first example, the first clutch unit is arranged to be partly engaged in a continuous slipping operation to drive the pump. The electronic control writ can be arranged to control the degree of slip in response to the determined lubricated state of the transmission, allowing the pump to be driven at variable speed depending on the lubrication requirement. Alternatively the electronic control unit can control the degree of slip to drive the pump at a predetermined, fixed speed.
According to a second example, the first clutch unit is arranged to be engaged intermittently to drive the pump. The electronic control unit can be arranged to control the rate of intermittent operation, that is, the duration and/or the frequency of clutch actuation, in response to the determined lubricated state of the transmission. The flow of lubricant supplied by the pump can be varied by control of the duration and/or frequency of clutch actuation.
In these examples the flow of lubricant supplied by the pump is reduced, in relation to normal operation, as the pump is being driven by partly engaging the inactive clutch. The vehicle transmission used in these examples is preferably a dual-clutch transmission.
The lubrication pump is arranged to be driven by the first input shaft by at least partly engaging the first clutch unit when the second clutch unit is engaged to drivingly connect the second input shaft to the driving wheels. In addition to normal dual-clutch operation where the first and second clutch units are used for gear shifting or power shifting, the invention is also applicable when the second clutch unit is engaged to connect the second input shaft to the driving wheels in a direct gear. In this example the electronic control unit is arranged to at least partly engaging the first clutch unit, in order to drive the first input shaft and the lubrication pump when the direct gear is used. The direct gear is commonly used when pulling up a hill, but may also be used at cruising speed. When running the vehicle in the direct gear, parts of the transmission, such as any overdrive gears are not driven, which reduces power loss and the need for lubrication. When required by the electronic control unit, the lubrication pump is driven by the first input shaft by at least partly engaging the first clutch unit. The invention as described in this and the above examples is preferably a commercial vehicle, such as a truck, a bus or a work vehicle.
The invention further relates to a method for operating a vehicle transmission in a vehicle. As indicated above, the transmission comprises a first transmission mechanism arranged to transmit mechanical driving power from an output shaft of at least one prime mover to a first input shaft and to put any one of a first set of gears in an engaged state to drivingly connect the first input shaft to the driving wheels, and a second transmission mechanism arranged to transmit mechanical driving power from the output shaft of the prime mover to a second input shaft and to put any one of a second set of gears in an engaged state to drivingly connect the second input shaft to the driving wheels. The transmission further comprises a controllable first clutch unit arranged to bring the output shaft of the prime mover and the first input shaft into engagement with each other, and a controllable second clutch unit arranged to brine the output shaft of the prime mover and the second input shaft into engagement with each other. As indicated above, the prime mover can be an internal combustion engine and/or an electric motor. A lubrication pump is drivingly connected to the first input shaft to lubricate the transmission and an electronic control unit is arranged to determine a lubricated state of the transmission and the operational state of the lubrication pump.
The method comprises the steps of:                registering the operational state of the first and second clutches and the lubrication pump,        driving the first input shaft and the lubrication pump by at least partly engaging the first clutch unit, when it is registered that the second clutch unit is engaged.        
As indicated above, the electronic control unit is used for registering the operational state of the first and second clutches and the lubrication pump. The electronic control unit is also used for controlling the operation of the lubrication pump by at least partly engaging the first clutch unit
According to a first example, the method involves partly engaging the first clutch unit in a continuous slipping mode to drive the pump. The degree of slip can be controlled in response to the determined lubricated state of the transmission. Depending on the lubrication state the degree of slip can be controlled to drive the pump at a predetermined speed, or at a continuously variable speed that is adjusted with the lubrication requirement.
According to a second example, the method involves partly engaging the first clutch unit in an intermittent mode to drive the pump. The electronic control unit can be arranged to control the rate of intermittent operation, that is, the duration and/or the frequency of clutch actuation, in response to the determined lubricated state of the transmission. The flow of lubricant supplied by the pump can be varied by control of the duration and/or frequency of clutch actuation.
The method can also comprise the farther steps of:
detecting the lubricated state of the transmission;
detecting if the first or the second clutch unit is actuated to connect the output shaft of the prime mover to the second input shaft; and, if it is detected that lubrication is required and that the second clutch is actuated,
controlling the first clutch unit to at least partly engage the first clutch to drive the pump.
The method described above is particularly useful for driving the lubrication pump using the first input shaft by at least partly engaging the first clutch unit when the second clutch unit is engaged to drivingly connect the second input shaft to the driving wheels in a direct gear. When running the vehicle in the direct gear, parts of the transmission, such as any overdrive gears are not driven, which reduces power loss and the need for lubrication. This will improve efficiency, but will cause the lubrication pump to stop when the first input shaft is not in use. Consequently, when lubrication is required, the lubrication pump can be operated using the above method.
The present invention also relates to a computer program, computer program product and a storage medium for a computer, all to be used with a computer for executing the method as described in any one of the above examples. The computer program comprises program code means for performing all the steps of the above method when said program is ran on a computer. The computer program product comprises program code means stored on a computer readable medium for performing all steps of anyone of the above method when said program product is run on a computer. The storage medium, such as a computer memory or a non-volatile data storage medium, is intended for use in a computing environment, the memory comprising a computer readable program code to perform the method.